Results

TRIAL 1

Table 1. Inverse energy at various angles – Trial 1

Figure 3. Trial 1 – The change of 1/ with respect to . The black dashes represent the trendline.

            The equation of the trendline of the graph in Figure 3 can be represented in the form of the modified Compton scattering equation:  
            The slope of the trendline may then be represented as , which also equals to 0.001925. Therefore, the rest mass of the electron equals:

            However, partway through Trial 1, I noticed the non-linearity of the points at the greater angles, which should not have happened. Theoretically, the relationship between 1/ and  is very linear, as can be seen from the modified Compton scattering equation. The non-linearity could easily skew the trendline, which would result in a significant error in the final calculations.
            This inaccuracy was attributed to the experimental setup. I noticed that the gap between the two lead blocks which shielded the front of the NaI detector was very wide. This meant that one part of the gamma rays which came in contact with the detector had a larger energy, and the other part of the gamma rays had a smaller energy than the energy of the gamma rays that scattered at angle . Even if these inaccuracies could have somehow cancelled each other out by the end, the result based on this kind of data cannot be fully trusted.
            I realized that even though it is impossible to eliminate this error completely, the error could be dramatically reduced by decreasing the space between the two lead blocks.
Instead of completing the data, I decided it would be best to move the two blocks closer together and simply start another trial.

TRIAL 2

Table 2. Inverse energy at various angles – Trial 2

 Figure 4. Trial 2 – The change of 1/ with respect to . The black dashes represent the trendline.

            As can be seen from Figure 4 above, the non-linearity error from Trial 1 is virtually unnoticeable, and all of the points do indeed seem to lie along the trendline.
            The slope of the line may be represented as , which also equals to 0.001931. Therefore, the inverse of the line’s slope will yield the rest mass of the electron, which equals to:

            This result is much reliable than the result from Trial 1, since the majority of the points do lie along a straight line, as the equation  predicts.